The government is to consider giving time for a bill to allow assisted dying if the director of public prosecutions fails to come up with clearer advice on when it is legal or illegal to help someone to die.

The issue resurfaced after the law lords ruled last week that Keir Starmer must produce clearer guidance on when prosecutions will be launched against those accompanying people who go abroad to kill themselves. Debbie Purdy, who has multiple sclerosis, had sought clarification over whether prosecutions would be brought in such cases. Purdy, who says the law on assisted suicide should be made "appropriate for the 21st century", has been fighting to protect her husband, Omar Puente, from potential prosecution.

A government source said: "Parliament is currently divided on this issue, but it may be that after Starmer produces his guidance, politicians will recognise that this is an ethical issue that cannot be left" to the Crown Prosecution Service alone.

Aiding and abetting suicide remains a crime punishable by up to 14 years' imprisonment. But none of the Britons who have helped terminally ill people die at clinics such as those run by Dignitas in Switzerland has been prosecuted.

Starmer, who has already decided that his guidance will apply equally to assisted suicides abroad and those in Britain, last night insisted that he would prefer Parliament to rule on the issue.

"We can't change the law, just fill in the policy," he told the Daily Telegraph. "That would require a change of the law. Not everyone has the means to go abroad to commit suicide, and a political decision has to be made on whether some assisted suicide is legal. That decision needs to be made by parliament."

He denied that the new guidelines would lead to more people travelling abroad to take their own lives, saying: "I don't think there are hundreds of people waiting to commit suicide depending on any policy I make."

Starmer also reiterated his position that the new guidelines would cover all acts of assisted suicide at home and abroad.

"We won't have separate rules for Dignitas," he added, referring to the Swiss clinic which has facilitated assisted suicides by Britons and other nationalities.

The leader of the house, Harriet Harman, spoke about the issue on BBC1's Andrew Marr Show over the weekend, saying she would be surprised if there were not more Commons debates on the issue. She also said the issue would be treated as a matter of conscience on a free vote, and that she would support the move.

Harman added she did not think the reform would represent a massive change in the law.

She spelled out her view that Starmer should produce guidance to make it clear when assisted dying is permissible. She said she expected the guidance to say that "if there is evidence that somebody's had a financial vested interest or if there's been pressure brought to bear, then there would of course be a prosecution".

Harman hinted there might be a need for legislation, saying the issue was "on the boundary between prosecutorial discretion and legislative definition".

Starmer hinted in his statement responding to the Purdy ruling that he would like to see a clear legislative framework.

The CPS has said it will draw up a detailed statement on the circumstances under which it would launch cases against those who help relatives die, as ordered by the law lords.

An interim policy will be published by the end of September before a public consultation and a final policy, in the absence of legislation, by the spring.

Harman added that she was very sympathetic to Purdy.

The former lord chancellor Lord Falconer last month tried to amend the coroners and justice bill to make assisted dying lawful if two doctors confirmed the person in question was terminally ill and deemed competent to make such a decision. His amendment was defeated in the House of Lords.

A poll of more than 1,700 people carried out for the campaign group Dignity in Dying found two-thirds supported a change in the law.